History,  Science

The Pressure Cooker

Pressure cooking is the process of cooking food at high pressure, employing water or a water-based cooking liquid, in a sealed vessel known as a pressure cooker. High pressure limits boiling and permits cooking temperatures well above 100 °C (212 °F) to be reached. Pressure cookers work by expelling air from the vessel, and trapping the steam produced from the boiling liquid inside. This raises the internal pressures and permits high cooking temperatures. This, together with high thermal heat transfer from the steam, cooks food far more quickly, often cooking in between half and a quarter the time for conventional boiling. After cooking the steam is released so that the vessel can be opened safely.

Denis Papin, (born Aug. 22, 1647, Blois, Fr.—died c. 1712, London, Eng.), French-born British physicist who invented the pressure cooker. In 1679 Papin invented his steam digester (pressure cooker), a closed vessel with a tightly fitting lid that confines the steam until a high pressure is generated, raising the boiling point of the water considerably. A safety valve of his own invention prevented explosions. Observing that the enclosed steam in his cooker tended to raise the lid, Papin conceived of the use of steam to drive a piston in a cylinder, the basic design for early steam engines; he never built an engine of his own.

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Papin, detail of an engraving, c. 1689 H. Roger-Viollet

Pressure cooker from tinned cast iron, made by Georg Gutbrod in Stuttgart, Germany. LA2-gutbrod-pressure-cooker-1864

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The process of tinning cast iron was a trade secret at the time, and the factory of Georg Gutbrod in Stuttgart was the only firm that could deliver pressure cookers in tinned cast iron. Other firms sold pressure cookers made from copper, plate, or untinned cast iron. Gutbrod offered pressure cookers in ten different sizes, sold in Sweden for between 3 and 20 riksdaler.

In 1918, Spain granted a patent for the pressure cooker to José Alix Martínez from Zaragoza. Martínez named it the olla exprés, literally “express cooking pot”, under patent number 71143 in the Boletín Official de la Propiedad Industrial. And in 1924 Jose’ Alix also wrote the first cookbook for the pressure cooker with 360 recipes.

In 1938, Alfred Vischer presented his invention, the Flex-Seal Speed Cooker, in New York City. Vischer’s pressure cooker was the first designed for home use, and its success led to competition among American and European manufacturers. At the 1939 New York World’s Fair, the National Pressure Cooker Company, later renamed National Presto Industries, introduced its own pressure cooker. Women were thrilled with this modern saucepan-style pressure cooker because it featured an easy-to-close interlocking cover, eliminating the need for awkward lug nuts and clamps. In the United States, “Presto” soon became the name synonymous with pressure cooking. The depression was over, and stores could not keep up with the demand for them. By the end of 1941, pressure cookers ranked among the largest producers of housewares dollar volume in leading stores throughout the country. At that time, there were 11 companies manufacturing pressure cookers.

Circa 1940 Presto Pressure cooker

In 1795, the French government offered a reward of 12,000 francs for anyone who could develop a method of preserving food supplies for the French armed forces. French confectioner Nicolas Appert took on the challenge and developed a canning process of packing food in clean jars sealed with a cork and cooking them in boiling water. This preservation method was accepted, and in 1809, Emperor Napoleon Bonaparte awarded Appert the prize money for inventing this basic canning process. Nicolas Appert then used his jackpot to open “The House of Appert,” the first commercial cannery in the world. These early discoveries, although crude, helped to develop the science of pressure cooking that we know today.

In general, the pressure cooker sterilization procedure is as follows:

  1. If you are sterilizing a sample in a container (eg: agar) make sure it doesn’t fill the container by more than two-thirds. Put the lid on the jars, but don’t close the lid has to be completely loose, if not the glass jar will explode. You can also cover jars and glassware with aluminum foil and keep it down with a piece of masking or autoclave tape.
  2. Fill the bottom of the pressure cooker with water to the depth of 1-2cm (not enough to start covering the base of the sample). This should be   de-ionised water, which can be gotten from the BioFabLab Laboratory, in the green taps that doesn’t have hot/cold symbols. Place a separator in the bottom of the pressure cooker so that the sample sits just on top of the water layer and is not directly touching the bottom of the cooker. In the video, we just used a spoon.
  3. Seal the pressure cooker and place it on a hot plate at high heat. Make sure the pressure valve is completely open.
  4. When steam begins to come out of the pressure valve opening, close it fully and turn the heat down to medium (approx. half the max). When pressure has built up inside the pot, and steam leaves through the pressure valve you can start the timer. The required sterilization time is usually 20-30 min.
  5. When the time is up, switch off the hot plate and remove the pressure cooker so it can cool down slowly for approx. 10-15min.
  6. Then, gradually open the pressure valve until steam has stopped coming out. With the Hawkins Big-Boy, this can be done by lifting the pressure cap slightly using a fork. If you release the steam to quickly, the sample will boil-explosively and spill the samples all over, and in worse case explode the glass containers.
  7. Open the pressure cooker, close the lids of the samples. Careful, it will be hot.

Petri dishes and other glassware are being sterilized in a pressure cooker in field laboratory. Clarence G. Thompson is pictured. Willapa Game Refuge. Naselle, Washington.

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  Photo by Wally C. Guy Date: July 19, 1963

After Pearl Harbor was bombed, World War II caused a halt to the manufacturing of pressure cookers because Aluminum was needed for the war. The War Production Board made steel available for use in manufacturing the pressure cookers. Women that worked in the defense plants found that the cooker made meal planning and cooking much easier. There were 50 or more new manufacturers producing some cheap, substandard cookers and selling them to unsuspecting consumers.

But, by the late 50s, the pressure cooker business wasn’t popular as it had been because the new manufacturers that emerged into this industry with inferior products and consumers that were using the cooker improperly were hurting the pressure cooker’s reputation, and its popularity began to wane.

The 60s and 70s produced yet more cooking inventions and cooking a quick and healthy meal was lost to these inventions but the reputable pressure cooker companies remained in business by continuing to improve their products and selling to the faithful customers who understood the benefits of pressure cooking.

In the 90s, when the world market opened, foreign manufacturers came roaring into the United States with many new styles and features, many in the “luxury model” category. The U.S. standard, however, continues to be the weighted valve regulator (or jiggle top). Virtually all the products on the market today adhere to the basic safety and cooking fundamentals of pressure cooking established by independent testing organizations. In the United States, the pressure cooker’s popularity continues to quietly resurface because, no matter what style you choose, it is still the best choice for providing quick, healthy “real meals,” and so much more.

Deborah Wilson  December 2019 #leavenopressurecookerbehind #museumwonders.com Sources: discoverpressurecooking.com/history.html En.wikipedia.org/wiki/pressure_cooking Fablab.ruc.dk/pressure-cooker-sterilization

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